Treatment of sugar solutions

ABSTRACT

Process for reducing the starch level of a starch-containing sucrose solution derived from sugar-bearing plant material, for example, a mill-clarified liquor or a refinery syrup, in which a thermostable bacterial amylase, such as one having Alpha amylase activity and being derived from the species Bacillus subtilis, is added to the solution at a temperature between 160* F. and the deactivation temperature of the amylase, the pH of the solution being neutral to slightly alkaline.

United States Patent Peter Hldl Klngsgrove, New South Wales;

Ian G. R. Burgess, Warrawee, New South Wales; Robin H.lloldgatgwahroonga, New South Wales, all of Australia Apr. 19, 1967Sept. 21, 1971 The Colonial Sugar Refining Company Limited Sydney, NewSouth Wales, Australia lnventors Appl. No. Filed Patented AssigneeTREATMENT OF SUGAR SOLUTIONS Niholson et al., International SugarJournal V60 p 260-263 (1958) Reed et aL, Enzymes in food Processing p50-59 Acidemic Press, New York, NY. 1966 Pigman, Ward, The Carbohydrates502-503 Academic Press, New York, 1957 Primary Examiner- Lionel M.Shapiro Attorneys-Emory L. Groff and Emory L. Groff, Jr.

pages ABSTRACT: Process for reducing the starch level of astarchcontaining sucrose solution derived from sugar-bearing plantmaterial, for example, a mill-clarified liquor or a refinery syrup, inwhich a thermostable bacterial amylase, such as one having a-amylaseactivity and being derived from the species Bacillus subtilis, is addedto the solution at a temperature between 160 F. and the deactivationtemperature of the amylase, the pH of the solution being neutral toslightly alkaline.

1 TREATMENT OF SUGAR SOLUTIONS Starch has been found to impede thefiltration of sugar solutions. In prior attempts to reduce the starchcontent of sugar solutions, it has been proposed variously to breedlow-starchcontent canes, to extract the juice from the canes bydiffusion (rather than by crushing) or to use low temperatures duringmaceration. It has also been proposed to reduce the starch content ofextracted juice by employing cold juice filtration or high-speedcentrifugation or by the use of thermolabile enzymes derived from maltor fungi.

However, all these prior processes have suffered from majordeficiencies, as a result of which none has been adopted in standardindustrial practice. in particular, the known treatment withthermolabile enzymes has required the use of temperatures below 160 F.and pH values less than 7. At such temperatures, starch which has notbeen heated previously above l60 F. exists in a granular form resistantto enzyme attack; and at such pH values, sucrose inversion is liable tooccur.

The main object of the present invention is to provide a simple, cheapand efficient process of improving the refining quality of sugarsolutions. Particular objects of the invention are to improve thefilterability of a sugar solution, the increase the optical clarity ofthe filtered solution, and to lower the viscosity of the solutionwhereby to improve the exhaustibility" of resultant molasses.

ln accordance with the invention these objects are achieved as a resultof reducing the starch level of starch-containing sucrose solution byadding to the solution at least one thermostable bacterial amylase, thetemperature of the solution being above 160 F. but below thedeactivation temperature of the amylase. The rate of reaction increasesrapidly with increase of temperature, and temperatures above 175 F. arepreferred.

It will be appreciated that the deactivation temperature of an amylaseis not sharply defined and that a practical upper limit for givenrequirements may readily be determined by experiment. The amylases whichare subject of the invention are active at elevates temperatures (e.g.190 F.) where the starch destruction rate is high.

Starch destruction rates achieved by the present invention are very muchgreater than those achieved by prior methods using thermolabileamylases. Correspondingly, the amount of amylase required and thereaction time are very much reduced. Two effects are responsible forthis improvement, (i) acceleration of destruction rate due to increasedtemperature, (ii) the fact that at temperatures above 160 F., starchexists in solution in a colloidal form particularly susceptible toenzymatic attack.

A further advantage of the present invention is that bacterial amylasestolerate conditions of pH (neutral to slightly alkaline) where inversiondoes not occur.

Preferred amylases are those possessing mainly a-amylase activity. Suchamylases are effect against both the branched as well as the linearfractions of starch, converting it to the following products: glucosemedium polymers, maltose and glucose. When B-amylases are used, actionis blocked at points of branching in the starch molecule and theproducts are essentially: high molecular weight dextrin and maltose.

Amylases especially favored for use in the invention are derived fromthe species Bacillus subtilis. These are nonpathogenic and are readilyavailable.

The amount of amylase required in a given case varies according to theactivity of the amylase preparation, the starch level obtaining in thesugar solution and the required degree of starch removal. In the case ofmost commercial amylase preparations and in the case of most naturallyoccurring starch levels in sugar solutions, quantities of amylasepreparation normally used vary between 5 to 750 partsper million (byweight) based on sucrose. The amylase is added as a solution, slurry orin powder form and is mixed thoroughly with the solution.

it is an additional advantage of the invention that required conditionsfor enzymatic starch destruction do not entail major deviations from theconventional sugar manufacturing process.

Usually, the selected amylase can be added to one of the normal processstreams of the sugar manufacturing process; however, it may be desirableto install holding vessels in certam cases.

lt has been found that the most suitable place for introducing theamylase into the sugar solution is in the third or fourth evaporatorvessels after the mill clarification process for the preparation of rawsugar. At these points, the temperature of the solution is about F., thepH lies within the range about 6.7 to about 8.2 (i.e. the optimum pHrange for bacterial amylase activity), and vigorous boiling (underreduced pressure) within the vessels ensures that the amylase isthoroughly mixed with the solution.

Experiments have shown that under these conditions, a reaction time aslittle as 5 minutes is sufficient to remove 30-80 percent of the starchoccurring in normal raw sugar mill process streams.

Reaction times other than 5 minutes are of course within the scope ofthe invention and it will be understood that the amylase can beintroduced alternatively at other stages in the sugar manufacturingprocess.

The invention is applicable to removing starch from sugar solutions notonly during mill processing but also during subsequent refining. ln thelatter situation temperatures of 180 F. are again normal and the pH liesusually within the range about 7.5 to about 8.5, i.e. the conditions arenot suitable for reducing the starch level by employing prior artthermolabile amylases derived, e.g. from malt. In addition, theseamylases do not work effectively at the high sugar concentrations (about55 to 70 Brix) which normally occur in refinery syrups, nor is theretrograded starch occurring therein susceptible to attack by them.

The present invention overcomes these disadvantages and permitssuccessful reduction of the starch level in the refinery situation.

The bacterial amylases selected for use in the practice of the inventionare of course not invertase-active, and it is a further advantage ofthis new process that it does not entail a detectable loss of sucrose.

The following examples illustrate applications of this process.

EXAMPLE 1 A cane with a high starch content known as variety N.Co 3l0was crushed, and the juice clarified in a pilot plant, ac-

cording to the usual procedure. After separation from mud,

TABLE 1 Treated Control Starch in clarified liquor (a) 154 920 Starch incrystallized sugar (b) 60 440 Starch in residual A-syrup (c) 445 L870Filterability of sugar, (d) 47 27 (a) pans per million by weight basedon solids in liquor.

(b) parts per million by weight.

(c) parts per million by weight based on solids in syrup.

(d) filterability expresses the filtration rate compared with that ofrefined sugar under conditions standardized to correlate with refineryperformance.

t l expressed as the optical density in n cm cell. of the unfilteredsolution llltfllslll'td against a blank of the filtered solution(filtration as defined In (p) above) at a wave length of 5.600 A.

Example 7 Super Rapidase" amylase preparation was introduced to thefourth evaporator vessel of a mill noted for a normal production of highstarch raw sugar. The addition was made during a period of one week atthe rate of 100 parts by weight of amylase per million parts by weightof sugar. The starch level of the raw sugar was progressively reduced asthe effects of the amylase spread through the intermediate mill processmaterials, and the filtration performanceof the sugar improvedcorrespondingly. The filtration performance of raw sugar made at thismill during the trail week was separately assessed at a carbonatationrefinery under carefully controlled constant conditions Results arerecorded in Table 6.

After the addition of amylase was terminated, the filtration performanceof the raw sugar deteriorated again as the starch level increased to thepretrail value.

(r) of the trial week. (5) parts per million by weight. ttl of thecarbonated raw liquor.

Examples 5 6 and 4 show the significant improvements can be achieved inthe refinery performance of raw sugars by treating the raw sugar(respectively) during refining or under laboratory conditions similar tothose obtaining in a refinery. The high heat stability of the appliedamylases permits some starch removal in the melter and storage tanks ofthe refinery without any significant alteration in the refining process.

These examples also show the high degree of the improvement obtained bya merely fractional starch removal. A comparison of the reduction instarch content and improvement in filterability from process liquors ofboth a mill and a refinery indicates that the amylase treatment is moreeffective in the mill (where a practical maximum of percent starchreduction may be achieved) than it is in the refinery (where a practicalmaximum of 50 percent starch reduction may be achieved). Reasons forthis are partly related to difficulty to the amylase in attacking theretrograded starch present in the refinery syrups.

What is claimed is:

l. A process for reducing the starch level of a starch-containingsucrose solution derived from a sugar cane comprising the step of addingto the solution at least one thermostable bacterial amylase, thetemperature of the solution being above F. but below the deactivationtemperature of the amylase and the pH of the solution being slightlyneutral to slightly alkaline thereby improving the filterability of saidsolution, increasing the optical clarity of the filtered solution andlowering the viscosity of the solution.

2. A process according to claim I wherein said thermostable bacterialamylase has (1- activity and is derived from the species Bacillussubtilis.

3. A process according to claim 1 wherein said temperature of thesolution is above F.

4. A process according to claim 1 applied to a starch-containingsucrose-containing sucrose solution which is an intermediate product inthe preparation of refined sugar from said 7. A process according toclaim 4 wherein the solution is a refinery syrup.

2. A process according to claim 1 wherein said thermostable bacterialamylase has Alpha - activity and is derived from the species Bacillussubtilis.
 3. A process according to claim 1 wherein said temperature ofthe solution is above 175* F.
 4. A process according to claim 1 appliedto a starch-containing sucrose-containing sucrose solution which is anintermediate product in the preparation of refined sugar from said sugarcane.
 5. A process according to claim 4 wherein the solution is amill-clarifIed liquor.
 6. A process corresponding to claim 5 applied tothe mill-clarified liquor contained in a vessel selected from the groupconsisting of the third and fourth evaporator vessels of a mill.
 7. Aprocess according to claim 4 wherein the solution is a refinery syrup.